1. Field of the Invention
The present invention principally relates to an optical waveguide component for use in optical communications and its manufacturing method.
2. Related art of the Invention
Optical communication systems using optical communications with a wide band characteristic and additionally having functions such as wavelength multiplexing transmission or bidirectional transmission are spreading among public communications, computer networks, or the like in order to obtain high speed and advanced function.
The optical communication systems are developing from a trunk line type to a subscriber type for general homes and offices. The homes and offices each require an optical network unit (ONU); an optical module is essential, which converts optical signals from a station into electric signals and receive them and which converts an electrical signal sent from the subscriber into an optical signals to transmit it to an optical fiber. Costs of the optical module must be lowered in order to diffuse optical fibers to the subscriber-type optical communication systems.
The wavelength division multiplexing method (WDM) is expected to allow optical fibers to be efficiently used to transmit more information. This method allows optical signals of multiple wavelengths to be transmitted through a single optical fiber to increase the amount of transmitted information in proportion to the number of wavelengths.
In dosing so, an optical module in each home requires a function to divide wavelengths.
FIG. 6 shows the configuration of an optical module for a general WDM. Main components of this module are an optical waveguide formed on Si substrate, an interference filter (a wavelength filter), a transmitting laser diode (LD), and a photodiode (PD) for reception or LD optical power monitoring.
The optical waveguide comprises a core embedded in a clad and having a relatively higher refractive index than peripheries thereof. Light propagates while being confined in the core of a high refractive index. By patterning the core into a circuit, functions such as branching and synthesis of light can be implemented.
In FIG. 6, light of wavelength 1.3 xcexcm and light of wavelength 1.55 xcexcm both from a station are multiplexed before transmission and then input to the optical module through a common port 67. The light of wavelength 1.3 xcexcm is used for bidirectional communications between the station and the subscriber, while the light of wavelength 1.55 xcexcm is used only for signal from the station to the subscriber. After these lights have passed through the optical waveguide, the light of wavelength 1.55 xcexcm is reflected by an interference filter 62 to leave the module through a port 2 (68), whereas the light of wavelength 1.3 xcexcm passes through a filter 62 and is then branched, so that a portion thereof is received by the receiving PD64 and converted into an electric signal.
On the other hand, for transmission, the LD63 is driven so as to be modulated to transmit an optical signal to the station through the common port 67.
Although such a conventional module is obtained by combining together a large number of parts such as lenses and prisms and accurately positioning them for assembly, the use of the optical waveguide as in the optical module in FIG. 6 can reduce the number of required part while diminishing the size of the module through assembly.
The module in FIG. 6, however, has the following problems in terms of costs and productivity:
One of the problems is high costs of the optical waveguide. FIG. 7 shows a procedure for manufacturing a general optical waveguide.
(a) A lower clad film 72 is formed on a silicon substrate 71 (film thickness: 20 xcexcm or larger). A core film 73 is formed thereon (about 10 xcexcm).
(b) The core film is formed in a predetermined pattern using photolithography or dry etching.
(c) Finally, an upper clad layer 74 is formed (film thickness: 20 xcexcm or larger).
In this manner, the thin films are deposited on the substrate 71 in the order of the lower clad, the core, and the upper clad. Processes for forming the thin films may include the flame deposition method, the CVD method, and the vacuum evaporation method. Since, however, the optical waveguide requires a large total thickness of about 50 xcexcm and must meet severe specifications as for film thickness accuracy, it requires a long tact time whatever process is used, resulting in insufficient productivity.
In addition, the patterning is required after the core film has been formed but uses a semiconductor process such as photolithography or dry etching, which requires expensive facilities and a long tact time. This process is thus unsuitable for mass production and does not allow costs to be reduced easily.
Another problem is the need to integrate the interference filter.
As shown in FIG. 6, the interference filter 62 has an important function for mutually separating wavelengths. The interference filter comprises a multilayer dielectric oxide film formed on a polyimide and is generally obtained by forming a groove in a substrate beforehand by means of dicing and inserting a filmed polyimide into the groove for adhesion and fixation.
Although the interference filter inherently has a high wavelength selectivity (isolation ratio), its performance varies due to various factors originating from the insertion and assembly of the polyimide into the groove. For example, FIG. 8 shows a polyimide substrate 81 inserted into a groove 83 as seen from above. The warpage or inclination of the polyimide substrate 81 inside the groove 83 slightly varies. an incident angle with respect to the filter, the position of reflected light, or the like, thereby varying a wavelength separation performance and transmission losses. The positional accuracy achieved when the groove is formed contributes to varying optical power obtained after light has passed through the filter. Reference numeral 82 denotes an optical waveguide and reference numeral 84 denotes an adhesive.
Accordingly, reducing such variations requires a very accurate assembly process, thereby unavoidably elongating the tact time and increasing facility costs. As a result, the current interference filter is unsuitable for mass production and does not allow costs to be reduced easily.
An optical module is also known which is obtained by cutting the optical waveguide at a predetermined position, interposing a wavelength filter at the cut position, and coupling the cut portions of the waveguide together again.
However, this module also requires a positional accuracy of xc2x11xcexc in reconnecting the cut portions of the optical waveguide. The position seems to be adjusted based on an outer diameter because the integral object is cut, but cut edges that may occur upon cutting may prevent the required accurate positioning despite the positioning based on the outer dimensions of the optical waveguide.
In view of the conventional problems, it is an object thereof to provide an optical waveguide part that enables the size and costs of an optical module to be easily reduced and a method for manufacturing this optical waveguide part.
Means for attaining,this object is shown below.
The 1st invention of the present invention is an optical waveguide part, wherein a plurality of optical members each having an optical waveguide groove are installed on a substrate with a fixing groove for fixing an optical fiber in such a manner that said optical waveguide grooves are connected together,
an optical element is located between the plurality of optical members with said optical waveguide groove, and
a recess of each of said optical waveguide grooves is filled with a material having a higher refractive index than said substrate and said optical member.
In this configuration, the substrate with the optical fiber-fixing groove functions as a lower clad. The plurality of optical members with the optical waveguide grooves function as an upper clad. In addition, the material placed in the groove functions as a core. When input from an end surface of the groove, light is confined in the groove if it meets specific conditions.
The optical waveguide part configured as described above does not require thin films to be deposited as in the prior art, thereby improving productivity. In addition, the optical fiber and the optical waveguide can be coupled together easily by placing the optical fiber in the fixing groove in the substrate also acting as the lower clad. Additionally, in this configuration, the optical waveguide grooves formed in the plurality of optical members are continuous, thereby enabling an optical element to be provided in a boundary portion between the optical members. The optical element is obtained by directly bonding the element on a substrate to the optical member or directly coating a thin film on an end surface of the optical member.
This configuration enables integration of any optical elements including wavelength filters, isolators, wavelength plates, and various mirrors.
This configuration also eliminates the needs for the groove into which the optical element is inserted as required in the prior art. Consequently, it can lower machining costs and substantially reduce variations in performance stemming from errors in integrating the optical element into the module.
The optical waveguide part according to the present invention is therefore advantageous in terms of costs and productivity.
The 2nd invention of the present invention is a process for manufacturing an optical waveguide part, comprising:
a first step of forming on a substrate a fixing groove for fixing an optical fiber and a first, second, . . . n-th (n is an integer of two or larger) optical waveguide grooves on a first, second, . . . n-th optical members, respectively;
a second step of coating a resin on said first optical member or said substrate, bonding said first optical member to said substrate on a surface thereof with said first optical waveguide groove formed therein, and hardening said resin;
a third step of additionally forming another optical element on an end surface of said first optical member; and
a fourth step of coating a resin on said second optical member or said substrate, bonding said second optical member to said substrate on a surface thereof with said second optical waveguide groove formed therein in a manner such that said first and second optical waveguide grooves are connected together, and hardening said resin,
wherein said third and fourth steps are also carried out on said third, . . . n-th optical members, respectively.
According to the present manufacturing method, the optical fiber-fixing groove and the optical waveguide groove in each optical member are produced, for example, by means of molding with a mold. Repeated molding with the same mold enables the mass production of optical members with the same groove pattern.
Alternatively, by coating a resin on an optical member or a substrate, bonding the optical member to the substrate on its groove pattern surface, and hardening the resin, the resin in the groove forms an optical waveguide core and bonds the optical member and the substrate together.
Each optical member and the substrate can be easily positioned with an accuracy of xc2x11xcexc using an alignment marker. The alignment marker can also be formed during the molding process.
In this manner, the optical waveguide part can be manufactured very easily. This manufacturing method comprises manufacturing the optical waveguide part by assembling the plurality of optical members on the base substrate with the fixing groove for the optical fiber; by directly forming a thin film in an interface between optical members, a large amount of parts with a wavelength separating function can be inexpensively manufactured.
The 3rd invention of the present invention is a process for manufacturing an optical waveguide part, comprising:
a first step of forming on a substrate a fixing groove for fixing an optical fiber and a first, second, . . . n-th (n is an integer of two or larger) optical waveguide grooves on a first, second, . . . n-th optical members, respectively;
a second step of directly joining said first optical member to said substrate on a surface thereof with said first optical waveguide groove formed therein;
a third step of filling said first optical waveguide groove with a core material;
a fourth step of additionally forming an optical element on an end surface of said first optical member;
a fifth step of directly joining said second optical member to said substrate on a surface thereof with said second optical waveguide groove formed therein in a manner such that said first and second optical waveguide grooves are connected together; and
a sixth step of filling said second optical waveguide groove with a core material,
wherein said fourth to sixth steps are also carried out on said third, . . . n-th optical members, respectively.
According to the present method for manufacturing the direct coupling is used to firmly bond the each optical member and the base substrate together, thereby substantially increasing mechanical strength.
The 4th invention of the present invention is the optical waveguide part wherein an optical waveguide groove is formed on a substrate, and recesses or projections for positioning are formed on a surface of said substrate at predetermined positions.
The 5th invention of the present invention is the optical waveguide part according to the 4th invention, wherein said recesses or projections are formed on a surface of said substrate which does not have said optical waveguide groove formed therein.
The 6th invention of the present invention is the optical waveguide part according to the 4th or 5th inventions, wherein said optical waveguide groove and said recesses or said projections are formed at one step by using a mold having projections or recesses on its surface.
The 7th invention of the present invention is a method for manufacturing an optical waveguide part comprising an optical waveguide groove on a substrate and recesses or projections for positioning formed on an end surface of said substrate, wherein:
an optical waveguide part material comprising the optical waveguide groove formed on a material substrate and recessed shapes or projected shapes formed on a surface of said material substrate has said recessed shape portions or said projected shape portions cut to manufacture said optical waveguide part.
The 8th invention of the present invention is a connection member for use in connecting together two optical waveguide parts according to any one of the 4th to 6th inventions.
The 9th invention of the present invention is the connection member according to the 8th invention, comprising a predetermined plate section having projections or recesses for connection that fit said recesses or projections on each of said two optical waveguide parts.
The 10th invention of the present invention is an optical part for connection together two optical waveguide parts according to any one of the 4th to 6th inventions, wherein:
said two optical waveguide parts each has said recesses formed in a site corresponding to an end surface of said substrate and having said optical waveguide groove formed therein, and
said optical part is fitted in said recesses formed in said end surface sections of said two optical waveguide part.
The 11th invention of the present invention is a method for connecting an optical waveguide part, wherein a connection member according to any one of the 4th to 6th inventions is used to connect together two optical waveguide parts according to claim 9 or 10 in a manner such that said optical waveguide grooves of said two optical waveguide parts are connected together.
The 12th invention of the present invention is a method for connecting an optical waveguide part, wherein an optical part according to any one of the 4th to 6th inventions is used to connect together two optical waveguide parts according to the 10th invention in a manner such that said optical waveguide grooves of said two optical waveguide parts are connected together.
The 13th invention of the present invention is an optical element comprising two optical waveguide parts according to any one of the 4th to 6th inventions connected together.
The 14th invention of the present inventions is the optical element according to the 13th invention, comprising an optical part located between said optical waveguide grooves of said two optical waveguide parts to optically connect said optical waveguide grooves of said two optical waveguide parts together.
The 15th invention of the present invention is the optical element according to the 13th invention, comprising an optical part located between said optical waveguide grooves of said two optical waveguide parts.